1. Field of the Invention
This invention relates generally to loadcells, and more specifically to an integrated loadcell system for accurately classifying an automotive driver/passenger.
2. Related Art
Airbag systems in vehicles often are fashioned to deploy all airbags when a crash occurs. If the passenger seat is empty or contains a child or other small occupant it is desirable to inhibit deployment since the airbag deployment may be useless or even counterproductive. It is thus necessary to accurately classify an automotive driver/passenger.
Loadcells are used to provide accurate measurements of compressive or tensile forces. Typically, the force creates a strain in the loadcell, which is measured by strain gage transducers. Accurate measurements, however, require that the force be applied along an axis, which is central to the load cell and about which all the transducers are symmetrically placed. Also, known loadcells, either with foil type gages or printed resistive inks, are utilized and the electronics are isolated from the sensors resulting in a low signal to noise ratio. Also, due to the inherently low gage factor of these sensors the full-scale output is low.
An example of a loadcell, which is sensitive to the effects of off-axis loading is known as a compression washer. An example of such a loadcell is in a product brochure entitled “Compression Only/Thru Hole Load Washer” and is disclosed in U.S. Pat. No. 4,212,360, the entire contents of which is incorporated herein by reference. An example of strain gauge transducers where the electronics are isolated from the sensors is disclosed in U.S. Pat. No. 5,942,695, the entire contents of which are incorporated herein by reference. Other examples of loadcells are disclosed in U.S. Pat. Nos. 5,714,695, 5,872,319 and 5,925,832, the entire contents of each of which is incorporated herein by reference.